Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/24/20
Area Forecast Discussion
National Weather Service Quad Cities IA IL
709 PM CST Wed Dec 23 2020
.UPDATE...
Issued at 701 PM CST Wed Dec 23 2020
Snow showers have continued to move into the area this evening.
Looking to the west, this trend is likely to continue through the
next 4 to 6 hours as the deformation zone begins to move north
and east through most of our Iowa counties. Pictures from CID show
a quick accumulation of a tenth or two of snow on the roads as
road temperatures have dropped quickly. Have increased QPF and pop
chances to cover these showers and likely accumulating snow in
our NW. The cams support this as well. The namnest is the most
aggressive with the showers and continue them across our area
towards daybreak. Current forecast is between the namnest and the
hrrr which quickly erodes precip between now and 3z. Concern this
evening is for slick surfaces with this light snow.
&&
.SYNOPSIS...
Issued at 259 PM CST Wed Dec 23 2020
Windy and unseasonably warm weather was found across the region
this afternoon. Strong southerly winds from 20 to 30 mph in the
warm sector and dry slot of a very strong, 986 mb low pressure
system over SE WI at 18Z, have boosted temperatures into the 40s
and 50s over the forecast area today. A few sites have exceeded
60, including Moline, which set a new record high for this date of
63 degrees, exceeding the old record of 60 set in 2015. Winds have
been gusting into the 40 to 50 mph range, having waned some after
an earlier surge with the passage of the upper level dry slot and
surface wind shift. This resulted in some gusts into the mid 50
mph range. Energy rotating around the upper level trough, centered
over the eastern Dakotas into NW IA, will drive the deep surface
low and on-going blizzard over NE, NW IA and MN northeastward into
the Upper Great Lakes Thursday. Over the local area, the
advancing upper trough and tight pressure gradient will keep windy
conditions in place overnight into Thursday. This NW flow will
push down the arctic airmass over the northern plains, where
afternoon temperatures were only in the single digits and teens.
&&
.SHORT TERM...(This Evening through Thursday)
ISSUED AT 259 PM CST Wed Dec 23 2020
Strong winds and bitter cold temperatures will remain the focus
through Christmas Eve. Will be keeping the Wind Advisory covering
the entire forecast area until 3 am unchanged for now. Winds will
remain strong, but we have likely already seen the highest gusts
for this event.
Tonight: Strong cold air advection was starting to be felt this
afternoon over eastern Iowa and will provide a sharp change
overnight into Thursday morning. Observations at 2 pm showed
temperatures only in the teens and 20s over NW IA and central IA,
which will rapidly overspread the forecast area this evening. Snow
in the deformation zone over NW IA, and some convective looking
radar returns and likely snow showers west of DMX will overspread
east central IA this evening, but likely in a weakening fashion
as the initial forcing exits northeastward. The idea of a light
dusting to possible half inch still looks supported, mainly
northwest of a line from Cedar Rapids to Dubuque overnight. A
steep low level lapse rate and arctic air should be sufficient to
produce flurries over the rest of the forecast area. Temperatures
will fall through the night to near zero to 5 above NW and 10 to
15 range SE. These readings combined with strong NW winds will
result in wind chills as low as zero to 15 below by sunrise and
possibly near 20 below toward mid morning along the IA highway 20
corridor.
Thursday/Christmas Eve: The surface pressure gradient gradually
weakens through the day while a vort max in the NW flow digs into
the upper level trough over the region. This will keep low cloud
cover in place and a favorable setup for at least occasional snow
flurries, especially east of the MS River. Temperatures will
remain nearly steady, rising perhaps only a few degrees, from the
single digits north to teens south through the day. This will be a
sharp contrast from today with most locations nearly 45 to 50
degrees colder than today.
.LONG TERM...(Thursday Night through Wednesday)
ISSUED AT 259 PM CST Wed Dec 23 2020
The bitter cold air on Christmas Eve will moderate some for
Christmas Day. Otherwise, conditions will be dry and brisk
northwest winds will finally diminish to around 10 to 15 mph for
Christmas Day. Thursday night will likely be the coldest of this
stretch, with widespread lows in the single digits, possibly
colder, depending on how fast the low clouds clear in the west as
a surface ridge builds in. Will keep a mention of at least window
dressing flurries or light snow over the IL side, where models
show there may be some lift from a vort wrapping around the
departing upper low. Christmas Day should see at least a gradual
clearing trend with the west most likely to see some sunshine.
Beyond, temperatures continue a day to day moderating trend
through Sunday. A weaker winter storm system will likely impact
the region late Sunday into Sunday night. Forecast confidence is
low with the timing and track of this system, but for now it looks
to be a rather dry system with minimal impacts. Near to slightly
below normal temperatures then follow early to mid week, when the
next, potentially strong storm system is progged to impact the
region. Forecast confidence remains low this far out, where the
national model blend and our forecast introduces chances for snow
Tuesday with high chance pops Tuesday night into Wednesday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
ISSUED AT 544 PM CST Wed Dec 23 2020
Gusty winds to persist through the period as gusts over 40 kts are
possible through the next few hours. MVFR deck moves in and then
the concern turns to snow showers. To the west pockets of snow
have reduced vsbys to IFR for a short period of time. This could
continue overnight and overspread our area. The ability to
forecast this at each TAF site is low so pilots and controllers
should be aware that this could happen quickly.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Wind Advisory until 3 AM CST Thursday for Benton-Buchanan-Cedar-
Clinton-Delaware-Des Moines-Dubuque-Henry IA-Iowa-Jackson-
Jefferson-Johnson-Jones-Keokuk-Lee-Linn-Louisa-Muscatine-
Scott-Van Buren-Washington.
IL...Wind Advisory until 3 AM CST Thursday for Bureau-Carroll-Hancock-
Henderson-Henry IL-Jo Daviess-McDonough-Mercer-Putnam-Rock
Island-Stephenson-Warren-Whiteside.
MO...Wind Advisory until 3 AM CST Thursday for Clark-Scotland.
&&
$$
UPDATE...Gibbs
SYNOPSIS...Sheets
SHORT TERM...Sheets
LONG TERM...Sheets
AVIATION...Gibbs
Area Forecast Discussion
National Weather Service Grand Rapids MI
643 PM EST Wed Dec 23 2020
LATEST UPDATE...
Aviation
.SYNOPSIS...
Issued at 323 PM EST Wed Dec 23 2020
-- Sharply colder after midnight, snow developing, hazardous travel
conditions near lakeshore --
-- Snow accumulations Christmas mainly in the morning --
&&
.DISCUSSION...(This evening through next Wednesday)
Issued at 323 PM EST Wed Dec 23 2020
-- Sharply colder after midnight, snow developing, hazardous travel
conditions near lakeshore --
Models continue to advertise a rapid drop in temperatures after
midnight into the 20s. As this happens precipitation will transition
to lake effect snow. As noted previously, this is not a slam-dunk
flash freeze setup, even though WSSI guidance certainly is
bullish. The uncertainty lies with unknown antecedent warmth and
wetness of roadways. Current radar indicates that relatively
meager precipitation is already exiting the area, so dry roadways
tonight are a real possibility.
What`s more certain is that visibility will be highly variable
and often poor due to transient lake effect snow bands and strong
winds capable of blowing the snow. A minority of short range
guidance -- specifically the 06Z,12Z (and now the 18Z) extended
HRRR runs -- show inch per hour accumulation rates persisting for
much of Thursday morning at places like Holland and Muskegon.
Having said that, I will add that the HRRR recently was upgraded to
version 4. During the HRRRv4 testing phase, it demonstrated superior
skill with lake effect snow. However, like with any model forecast,
accuracy with details first depends on accuracy with larger scale
features. The next 24-48 hours will be our first real opportunity
to assess HRRRv4 performance with lake effect in real time.
Should be interesting.
-- Snow accumulations Christmas mainly in the morning --
Much of far southwest Lower Michigan -- including Ottawa, Van
Buren, and far western Kalamazoo Counties -- will likely see
intense snowfall beginning shortly after midnight Christmas
morning when an already active lake effect snow regime gets a
substantial boost from surface based frontogenesis resulting from
cold air wrapping around Lake Michigan up into this area. For this
reason, have added Barry and Van Buren counties to the advisory.
We also have extended the advisory for Lake/Newaygo/Kent Counties,
although Kent probably wont see as much extra accumulations as
its counties immediately north and south.
East of US-131, particularly south of I-96, snow showers are
possible Christmas afternoon with the inland extension of some snow
bands. However, little if any accumulations are expected.
-- Monday morning commute possibly affected by Sunday system --
As noted previously, there is much uncertainty here regarding
evolution and track. Regardless, this will be our next system to
assess after Christmas.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 641 PM EST Wed Dec 23 2020
Ceilings are lowering as warm and moist southerly winds bring rain
toward our area. MVFR conditions will dominate this evening before
winds switch to the west by midnight and rain changes to snow.
This switch to snow will bring cloud bases down even more, as well
as visibilities. Snowy and wintry conditions will continue all day
Thursday, especially the closer you get to Lake Michigan. Thus,
Lansing and Jackson will see the best conditions, and have the
highest chance of seeing VFR conditions develop by Thursday
afternoon.
&&
.MARINE...
Issued at 337 PM EST Wed Dec 23 2020
No changes to the previous forecast. Shore-parallel flow will
limit the threat for lakeshore flooding. There will be a
window for freezing spray Thursday into Friday, but the window
will be small due to colder temperatures lagging the strongest
winds a bit.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 4 AM Thursday to 7 PM EST Friday
for MIZ037-038-043-044-050-056-057-064-065-071-072.
LM...Gale Warning until 1 AM EST Thursday for LMZ844>849.
&&
$$
SYNOPSIS...TJT
DISCUSSION...TJT
AVIATION...AMD
MARINE...TJT
Area Forecast Discussion
National Weather Service Lincoln IL
747 PM CST Wed Dec 23 2020
.SYNOPSIS...
Issued at 231 PM CST Wed Dec 23 2020
A powerful storm system moving through the middle of the country
will draw in the coldest air of the year, just in time for the
holiday. High temperatures will only be in the teens and 20s for
Christmas Eve and Christmas Day, and wind chills below zero are
likely for Christmas morning. Showers and isolated thunderstorms
will accompany the front through early evening, with scattered
snow flurries overnight into Thursday.
&&
.UPDATE...
Issued at 741 PM CST Wed Dec 23 2020
Just before 800 PM this evening, a strong cold front is shifting
east across the I-57 corridor accompanied by about a 2 hour
window of showers. Near the frontal trough there is a relative
lull in wind speeds, but behind the front expect steepening low
level lapse rates due to strong cold advection, moderate pressure
rises of 2-5 mb/3hr, and tightening of the pressure gradient
which will all contribute to winds picking back up again. At this
time, no changes are planned for ongoing wind advisory headlines
though gusts may only sporadically reach criteria.
&&
.SHORT TERM...(This evening through Thursday)
ISSUED AT 231 PM CST Wed Dec 23 2020
Strong cold front is knocking on our doorstep, with 1 pm surface
analysis showing it about to cross the Iowa border. Some earlier
clearing has made its way over to the Taylorville to Champaign
area, helping to mix down the low level jet. Have seen several
wind gusts near or just above 50 mph from Decatur and Bloomington
eastward. A narrow line of convective showers has formed ahead of
the front near the Illinois River, and will advance across the
forecast area through mid evening. GOES lightning mapper recently
showed a few strikes northwest of Peoria, and a few hundreds of
MUCAPE are progged by the RAP model to clip the southeast CWA this
evening. With the strong dynamics in place, have added a mention
of isolated thunder to accompany the front.
Temperatures have fallen into the 30s in southeast Iowa and were
in the teens as close as Des Moines, so no significant changes are
planned with temps into Thursday. We did reach 60 degrees in a
large area of west of I-55, but temps should be below freezing in
all areas west of I-57 by midnight and in the teens by morning
along and north of I-72. Wind chills should be in the single
digits in most areas by morning and are not likely to recover much
during the day Thursday.
Regarding the wind headlines, no changes are planned at this time.
Areas south of I-70 have struggled quite a bit to get close to
criteria thus far, but HRRR guidance continues to support some
40-45 mph gusts early this evening as the front arrives.
.LONG TERM...(Thursday night through Wednesday)
ISSUED AT 231 PM CST Wed Dec 23 2020
Not quite North Pole levels, but temperatures for Christmas
morning still look to be in the single digits in most areas, with
wind chills below zero. However, the cold core aloft quickly moves
off to the east, and temperatures Friday night should be fairly
steady or drift upward a bit. Warm air advection should help get
us back to 40 on Saturday.
A couple systems of note in the extended range. The Sunday cold
front looks to be mainly dry in our area, but a rather potent
storm system appears to take shape over the central Plains on
Wednesday. Longer range models are in decent agreement considering
the distant time frame, with precipitation types a concern. Plenty
of time for evaluation, though.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 524 PM CST Wed Dec 23 2020
A cold front is moving across central Illinois this evening
bringing showers, gusty winds, and MVFR conditions. Strong south
winds ahead of the front will veer to the NW with passage, but
remain strong with gusts up to around 30 kt expected overnight.
MVFR ceilings and visibility will accompany about a two hour
window of showers with the front. MVFR or near MVFR ceilings are
possible again overnight, but may be patchy or short lived. Winds
will taper some Thursday but remain breezy with gusts into the low
to mid 20 kt range.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 10 PM CST this evening for ILZ044>046-
052>057-061>063-066>068-071>073.
Wind Advisory until 3 AM CST Thursday for ILZ027>031-036>038-
040>043-047>051.
&&
$$
UPDATE...Deubelbeiss
SYNOPSIS...Geelhart
SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Deubelbeiss
Area Forecast Discussion
National Weather Service Paducah KY
545 PM CST Wed Dec 23 2020
.UPDATE...
Issued at 533 PM CST Wed Dec 23 2020
Updated aviation discussion for 00z TAFs.
&&
.SHORT TERM...(Tonight through Friday night)
Issued at 345 PM CST Wed Dec 23 2020
Main challenge during the first period (today) has been addressing
momentum transfer with winds in advance of the cold front over
central Missouri this afternoon. Convective transfer from showers
has also supported some locally higher wind gusts this afternoon.
There has been a signal for wind gusts around 40 mph over mainly
the Pennyrile region late this afternoon and this evening. Decided
to go ahead and issue a Wind Advisory through midnight for the
most of the west Kentucky Pennyrile, a small part of the Purchase
Area of west Kentucky near the Land Between the Lakes, and Spencer
County in southwest Indiana. Anticipate most of the strongest
winds will shift toward a Hopkinsville to Owensboro Kentucky line
between 02z-04z Thursday (8-10 pm CST Wednesday). If the wind
gusts perform lower than expected, the evening forecast crew may
need to cancel the advisory earlier.
RAP guidance still shows the potential for isolated elevated
thunderstorms late this afternoon and this evening. Decided to
leave a mention of isolated thunderstorms in the forecast for
parts of southeast Illinois, southwest Indiana, and west Kentucky
through this evening.
It looks like precipitation will move out over the southeast Pennyrile
at least one to two hours before sub-freezing air moves into that
region shortly before 12z Thursday ( 6am Thursday). Road
temperatures and surface temperatures will need to be monitored
for flash freeze potential, but any wintry precipitation (snow)
impacts will be negligible.
Temperature trends through Christmas evening still looks to be on
track. Adjusted dewpoints downward a little bit to reflect the
much drier air infiltrating into the region. The drier boundary
layer air may impact the potential and/or coverage of any snow
flurries Thursday or Friday.
Plan to continue to highlight wind chills for late Thursday night
and Friday in the Hazardous Weather Outlook. Given the relatively
elevated wind chills we have had during the late Fall and early
Winter, this will be a wake-up call for travelers and persons at
home outdoors on Christmas Day.
.LONG TERM...(Saturday through Wednesday)
Issued at 345 PM CST Wed Dec 23 2020
The long term forecast begins with the departure of the Christmas
trough, leading to a significant warming of temperatures with highs
back into the mid to upper 40s Saturday. Dry weather continues into
Sunday with slight ridging over the Lower Ohio Valley. Winds will be
breezy Sunday ahead of a shortwave that is expected to pass to the
north Sunday night. Moisture amounts are fairly meager in both the
ECMWF and North American ensembles, though the GFS is the only
ensemble with a large percentage of members showing measurable
precip. As such, precip is limited in this forecast to a slight
chance of light rain Sunday night, with some mixing of light snow
possible north/west of the Ohio River.
Immediately following the shortwave low, temperatures will decrease
with the brief period of shortwave troughing over the Quad State.
Lows Monday night will drop into the 20s, nudged slightly upwards
away from the GFS towards the Canadian and ECMWF ensembles.
The active upper-level flow will continue into midweek. A surface
high will quickly follow behind the shortwave low across the Great
lakes, bringing northeasterly flow across the Quad State Tuesday,
keeping highs down near 40. A much stronger upper-level low in the
Four Corners will undergo surface cyclogenesis in the Plains late
Tuesday into Wednesday. Ensembles show significant mid-level
moisture levels starting Tuesday night ahead of the system as flow
turns towards southerly. The most prominent 500-mb height ensemble
cluster favors, especially in the Canadian, a slower eastward
progression of this system. Uncertainty is high enough to keep some
PoPs in Tuesday, but the bulk of the precip is not expected until
later Wednesday along with breezy winds.
&&
.AVIATION...
Issued at 533 PM CST Wed Dec 23 2020
Cold front will sweep through the region this evening. SHRA and
associated reduced vsbys will end from west to east between
01-07z, with only some lingering light showers possible after 07z
in our east. Winds will switch around from S to WNW and remain
fairly stout through the night, although we should gradually lose
our gusts. Appears we may return some gusts through the day
tomorrow, but generally remaining below 20 kts. MVFR, and brief
IFR, cigs will improve to VFR territory first at KCGI/KMVN around
03z and eventually at KEVV/KOWB closer to 07z. Guidance is hinting
at a return to higher range MVFR cigs at KEVV/KOWB tomorrow
morning, which may eventually lift to low VFR range by afternoon.
&&
.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...Wind Advisory until midnight CST tonight for INZ088.
KY...Wind Advisory until midnight CST tonight for KYZ007>013-015>017-
019>022.
&&
$$
UPDATE...SP
SHORT TERM...Smith
LONG TERM...ATL
AVIATION...SP